4 Oct

As a previous post explained, oil temperature is fed into an analog input on the dash, and that the value recently started reading “51 deg C” when cold. The dash allows setting up sensors as either resistance-based or voltage-based. It turns out that the sensor was set as resistance-based, but because the ECU already has a pull-up resistor on the sensor, that’s a voltage, so it has to be voltage-based. How on Earth it worked fine for five months and only now started acting up is beyond me. I don’t touch the dash configuration unless necessary, but today the sensor type was switched to voltage and presto, it started working… again. Very odd.

The other issue which has been going on even longer is that dash MAP reads low. The ECU always sees the correct value yet the dash reads low (only) at idle. As posted earlier, I thought the dash used the MAP value in the CAN packet but I forgot that I had to give up on it because the dash scales MAP as a percent and I can’t change it – percent what!?). I spoke to AiM and they said to check that the dash has the latest code – it does. They also said to connect the sensor ground of the dash to the sensor ground of the sensor, so I connected the two. Got everything buttoned up and started the car, and it idled like crap. I let it warm up and it just kept running worse and worse, so an earlier tune that I knew worked fine was loaded – it ran like crap as well. Then, the light bulb went on, and I remembered having this same problem when I connected the flex sensor ground to sensor ground (imagine that) and it also ran like crap. Sure enough, disconnected the ground and the engine idled perfectly smooth. I tried grounding the dash input signal ground straight to the chassis and it didn’t make any difference to the displayed value. On the other hand, the displayed value was displaying fine, so not sure what’s going on there.

Drove the car some yesterday and if it wasn’t for the MAP-drop thing, it’s running great! Just have to get that behind me!